230 CORALS AND CORAL ISLANDS. 
Society of Edinburgh (vol. xvi., 1845), it is stated as a deduc- 
tion from two hundred and sixty-seven experiments, extend- 
ing over twenty-three successive months, that the average 
force for Skerryvore, for five of the summer months, during 
the years 1843, 1844, was six hundred and eleven pounds per * 
square foot; and for six of the winter months of the same 
year, it was two thousand and eighty-six pounds per square 
foot, or three times as great as during the summer months. 
During a westerly gale, at the same place, in March, 1845, a 
pressure of six thousand and eighty-three pounds was regis- 
tered by Mr. Stevenson’s dynamometer (the name of the in- 
strument used). He mentions several remarkable instances 
of transported blocks. 
We must, therefore, allow that some effect will be pro- 
duced upon the coral groves. There will be trees prostrated 
by gales, as on land, fragments scattered, and fragmentary 
and sand accumulations commenced. Besides, masses of the 
heavier corals within ten to twenty feet of the surface may 
be uptorn, and carried along over the coral plantation, which 
will destroy and grind down every thing in their way. So 
many are the accidents of this kind to which zodphytes ap- 
pear to be exposed, that we might believe they would often be 
exterminated, were they not singularly tenacious of life, and 
ready to sprout anew on any rock where they may find quiet 
long enough to give themselves again a firm attachment. 
But it should be observed, that the sea would have far 
less effect upon the slender forms characterizing many z00- 
phytes, among which the water finds free passage, than on the 
massive rock, against whose sides a large volume may drive 
unbroken. Moreover, much the greater part of the strength 
of the ocean is exerted near tide level, where it rises in break- 
ers which plunge against the shores. Yet owing to the many 

